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Appendix   VI.

1207

small cylindrical chamber D is connected at bottom to a point just
under the delivery valve, and at top to the air vessel. The rise
and fall of water in B acts as a liquid piston to draw in air at E and
deliver it into the air vessel, while cock A adjusts the action, c
and i> are glass gauges.



Jl/ir Y

1062.

P. T28 The Centrifugal Pump.—The diagram of pump
efficiencies, p. 734, shews that a single pump is unfit for high
lifts because of the rapidly decreasing economy at »««*<*
pressure. The difficuky can be overcome by compounding that
Iplacing two or more pumps m series, so that the pressure-head
obtSSd finally is the aggregate of those due to each^purnp.